Geology Reference
In-Depth Information
In what follows, the authors describe the peculiarities of key minerals paying
special attention to the best available practices and emphasising the associated en-
vironmental impacts and energy costs. Among the significant references, the reader
can consult the Ullmann's Encyclopedia (Ullmann and Gerhartz, 2002), the BREFs
(Best available techniques Reference Documents) entitled “Reference Document on
Best Available Techniques in the Non-Ferrous Metals Industries, 2009” (IPPC, 2009)
and “Reference Document on Best Available Techniques on the production of Iron
and Steel”, (IPPC, 2001, 2012), Wills and Napier-Munn (2011) or the Ecoinvent
database (Classen et al., 2007). In addition, detailed information about geoche-
mistry and main uses for each individual element can be found in Sec. B.2 in the
Appendix.
The minerals described are sorted by industrial relevance in terms of historical
production and grouped according to their ore and/or final use.
8.2 Iron and steel
8.2.1 Process
Steel production is derived from the carbon reduction of hematite (Fe
2
O
3
) and
magnetite (Fe
3
O
4
) ores. Although there are other routes, most from ores comes
via the blast furnace/basic oxygen furnace. The blast furnace is the centre of the
process where all the steelworks are integrated and is maintained at temperatures
of 2000
o
C to 2300
o
C. The ores and iron pellets are the major raw materials fed
into the blast furnace. They are designed to comply with an appropriate size and
hardness. It is also fed by alternate layers of coke and coal followed by sinter ore
and limestone. The former is produced in an agglomeration process that recycles
fine dust particles with residues and additives to charge the blast furnace. The
latter is the main constituent of the flux that melts silicon dioxide impurities in
the ore and is decarbonised and converted into calcium oxide in the middle zone
of the furnace. This calcium oxide then reacts with the silica contained in the
ore to produce calcium silicate that forms a liquid slag. The slag is pelletised and
commonly sold to cement plants as an additive for road construction.
Coke meanwhile is produced in a coke oven gas (COG) and is obtained by
coal pyrolysis i.e. the heating of coal in an oxygen-free atmosphere. It is a better
fuel and reducing agent than natural coal. As the reduction process is completed by
oxidation of carbon monoxide, a great blast of pre-heated air (around 1200
o
C) needs
to be injected into the bottom of the furnace- approximately 4 tonnes per tonne of
liquid iron. This partially oxidises the coke to carbon monoxide and produces the
heat needed to maintain the temperature whilst the carbon monoxide reduces the
iron oxides to produce liquid iron. This “hot metal” and the less dense molten slag
are tapped off separately from the bottom of the furnace
1
.
1
See http : ==www:thepotteries:org=shelton=blast_furnace:htm. Accessed Nov. 2011.
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